Particulate methane monooxygenase (pMMO), a membrane bound protein found in methanotrophic bacteria exhibits a broad range of biological activity. pMMO catalyzes the dioxygen-dependent, two-electron oxidation of methane to methanol. Though some of the chemistry of this enzyme is well-defined, the structural, physical, and functional characteristics of its multiple copper ions remain unclear. Advances in the preparation and enzymological treatment of M. capsulatus (Bath) pMMO offer the potential for the first XAS structural characterization of two functionally distinct Cu cluster sets: C-clusters (i.e. "catalytic" clusters which react with O2), and E-clusters (believed to assist in electron-transfer to the C-clusters). Chemical treatments which will isolate one of these two sets of clusters (in particular the C-clusters) will be undertaken and selectively probed via XAS.